The present invention reltes to a heating device of a hot-air circulating microwave oven using a shape memory alloy for the damper driver spring.
When a shape memory alloy mainly composed of either titanium or nickel is heated by directly being connected to the power source, energy is generated to enable the alloy to return to the shape originally memorized. A technique has been proposed or applying such energy to the damper driver spring for opening and closing the ventilation hole provided in the chamber of a hot-air circulating microwave oven.
However, since the shape memory alloy performs the same operation as returning to its original shape by directly receiving the power when peripheral temperature rises, and as a result, being thermally affected by the chamber temperature of a microwave oven, such a shape memory alloy may malfunction to cause the damper to either open or close itself incorrectly. For example, if the damper closes itself while a microwave heating is performed by opening the damper for ventilating cooling air into the chamber, humid vapour generated by food cannot be fully exhausted out of the chamber, causing the chamber door glass to become cloudy.
On the other hand, since the shape memory alloy also moves as the damper moves, if a stationary terminal is set to an end of the shape memory alloy, since tracks of the damper lid that follows the opening and closing movement of the damper and the shape memory alloy spring cannot be identical to each other, a force needed for causing the heated shape memory alloy to return to the originally memorized shape cannot be transmitted to the damper lid sufficiently.
Although both ends of the shape memory alloy spring and the power supply line can be easily installed via terminals by employing caulking means, being affected by the movement of the damper lid, the caulked strength of the terminal lowered. This causes the damper to unreliably perform the opening and closing operations during cooking in a microwave oven via microwave heating or oven heating using a heater.